The PDIFF beamline is dedicated to diffraction experiments on bulk polycrystalline materials, with the emphasis on in-situ investigations. Additional experimental facilities enable high-resolution powder diffraction, residual stress and texture measurements. In specific cases the beamline is also suited to scattering studies on thin-films and epitaxial layers.

The experimental facilities consists two experimental stations - a large 3-circle powder diffractometer which is equipped with detectors for rapid data-acquisition and can carry heavy loads such as customised sample-conditioning equipment. A smaller 4-circle diffractometer with a high-resolution anaylser is available for experiments requiring additional degrees of freedom for the sample (but with limited facilities for sample conditioning.)

a heavy-duty 3-circle powder diffractometer capable of carrying sample loads up to approx. 60kg together with multiple detector systems for real-time investigation of structural changes in polycrystalline materials. Experiments can be carried out on small sample quantities (a few milligrams) in either transmission or reflection geometries. The diffractometer is equipped with 2 main detectors: a large CCD camera and a 90° 1D detector for simultaneous registration of x-ray scattering over a large angular range.

a 4-circle Kappa diffractometer for experiments requiring additional orientational degrees of freedom, for example for texture and stress analyses in thin films. This diffractometer can carry up to approx. 5 kg loads and is equipped with either analyser or Soller collimator optics for high angular resolution studies. While the instrument is normally equipped with detectors optimised for angular and energy resolution it can also be equipped with CCD or 1D linear detectors.

Various diffraction geometries can be accommodated: symmetric and asymmetric reflection and transmission, both with and without continuous sample rotation. Typical time resolution for in-situ studies depends both upon the sample and the detector setup, but can be down to the order of 0.5 second for powder patterns recorded with either 1D or 2D detectors. Typical measurement times for high-resolution powder scans are between 2 and 6 hours depending on the sample scattering power. Spatial resolution (at the sample) is of the order of 100µm.

Instrumentation

Various diffraction geometries can be accommodated: symmetric and asymmetric reflection and transmission, both with and without continuous sample rotation. Typical time resolution for in-situ studies depends both upon the sample and the detector setup, but can be down to the order of 0.5 second for powder patterns recorded with either 1D or 2D detectors. Typical measurement times for high-resolution powder scans are between 2 and 6 hours depending on the sample scattering power. Spatial resolution (at the sample) is of the order of 100µm.

The heavy-duty powder diffractometer is equipped with 3 concentric axes: two of these carry various detector combinations while the third can carry a sample load of up to ≈ 60kg. The detector circles are independent so that diffraction data can be collected simultaneously by more than one detector system.

The heavy-duty powder instrument is based on 3 concentric rotation axes:

Detector circle 1 carries a Princeton CCD detector.

Detector circle 2 carries a 90° curved PSD (Inel CPS590)

The sample circle allows masses of up to 80kg to be mounted

An XYZ-stage for sample mounting and adjustment is available as is a multi-sample changer for powders (flat-plate, reflection). A small Eulerian cradle is planned to be instlled in 2014.

The instrument is equipped with a single analyser channel (Ge111-crystal) and NaI scintillation detector. It is also possible to equip the diffractometer with both the CCD camera and the 90°PSD.

Due to construction and space limitations the sample stage can carry a maximum of 10kg load and is therefore unsuitable for heavier sample-specific instrumentation.

Detectors

A selection of detectors suited to various polycrystalline diffraction experiments is available. Depending on parameters such as angular and energy resolution, data-acquisition speed and sample form and quantity the best type of detector can be matched to the experiment. At present the following detectors are available for both instruments:

Princeton 165mm diameter 2D-CCD detector

INEL 90° linear PSD

Vantec-1 PSD

NaI point detectors (from mid-2009 a 3-axis multi-analyser stage will be available for simultaneous registration of high-resolution data)

Sample conditioning & manipulation

A variety of sample holders are available for ambient temperature transmission & reflection measurements. Additionally a furnace to ≈1200°C and an LN2-cryostat to ≈80K are available for reflection samples. A capillary furnace and a tensile extension/compression stage will be available from May 2009.

Software

A full range of general purpose XRD routines for powder data analysis, cell refinement, phase analysis and structure refinement (eg. Fullprof & Topas) are available. On-line databanks available at the beamline include the ICSD, PDF and CSD.

Characteristics

The beamline optic delivers focused monochromatic radiation to two experimental stations – a heavy duty 3-axis powder diffractometer and a 4-circle Kappa-goniostat. The experimental stations are accessible in an either/or mode. The re-configuration of the beamline when switching between stations is around 1-2 hours depending on the beam parameters required and the complexity of the detector setup.

Flux at sample position
≈2x1010 ph/s/mm2 at 10keV, based on 100mA beam current and 0.1% bandwidth

Beam size at sample
≈0.5mm (H) x .5mm (V) (focused), ≈0.5mm (H) x 1mm (V) collimating (fwhm).
The vertical focus point can be optimised for either the 1st or the 2nd experiment based on the bending radius of the mirror. The horizontal focus is optimised for the 1st experimental station